1. Field of the Invention
The present invention relates to a zoom microscope used for vertical observation and acquisition of a specimen image.
2. Description of the Related Art
A known zoom microscope is structured by combining a zoom imaging lens with an infinity correction objective lens (see, for example, Japanese Unexamined Patent Application Publication No. Hei 6-18784). In this structure, observation magnification of a specimen image is arbitrarily variable by moving a variable-power lens group in the zoom imaging lens in an optical axis direction.
Further, it has been proposed that a zoom microscope is structured by attaching an infinity correction zoom objective lens to a revolver of a typical microscope, thereby combining the zoom objective lens and an imaging lens of the microscope (see, for example, Japanese Unexamined Patent Application Publication No. 2004-133341). In such a structure, observation magnification of a specimen image is arbitrarily variable by moving a variable-power lens group in the zoom objective lens in an optical axis direction.
However, intended variable-power ranges of both of the aforesaid zoom microscopes are narrow, and they do not include a low variable power, for example, (about 0.5 to about 2). The expansion of the variable-power range (for example, to the low-power side) is desirable, however, it is difficult for the zoom microscope of the former document to set the position of an entrance pupil of the objective lens at infinity over the entire variable-power range since a pupil of the objective lens is in the zoom imaging lens and the position of the pupil of the zoom imaging lens moves due to the power variation. On the other hand, in the zoom microscope of the latter document a pupil is located between an objective lens portion and a zoom portion (including the variable-power lens group) in the zoom objective lens, so that it is possible to provide a plurality of zoom objective lenses of different variable-power ranges, and expand the variable-power range by selectively attaching them to the revolver. However, there is a disadvantage that the provision of the zoom portion for each zoom objective lens results in increasing the scale of the device substantially.